I know this is a really old post. But I came across the same issue today.
"Admin action: Redelivering the message failed, due to: java.lang.Exception: Message already in admin action or locked by message version editor"
And found the real solution after scratching my head for hours. 
Just Go to monitoring --- > Adapter Engine Status -- > Database locks
And delete the lock on that message ID. And then try cancelling it again.
BTW I'm on 7.3 single stack.
Hope this will help another poor soul.... 